Conventional laser Doppler velocimeters (“LDVs”) transmit light to a target region (e.g., into the atmosphere) and receive a portion of that light after it has scattered or reflected from the target region or scatterers in the target region. This received light is processed by the LDV to obtain the Doppler frequency shift, fD. The LDV conveys the velocity of the target relative to the LDV, v, by the relationship v=(0.5)cfD/ft where ft is the frequency of the transmitted light, and c is the speed of light in the medium between the LDV and the target.
LDV's are have a wide range of applications including, but not limited to: blood-flow measurements, speed-limit enforcement, spaceship navigation, projectile tracking, and air-speed measurement. In the latter case the target consists of aerosols (resulting in Mie scattering), or the air molecules themselves (resulting in Rayleigh scattering).
Conventional LDVs for meteorological measurements or applications generally incorporate a single motorized telescope that takes measurements sequentially along different axes, or use three telescopes, switching from one to the next, and so on, to allow sequential measurements along the different axes. This approach is disadvantageous in that is does not enable simultaneous measurements of three components of velocity.